My Sick Bird

I am new to chickens and have a small flock of 7. One of the younger hens is now coming down with respiratory issues. She has bubbles in one of her eyes, which is now closed, her breathing is labored and she's wheezing and lethargic. I used Vet Rx, which I got from Aubuchon Hardware, but am not sure how effective it will be. Is there anything else I should be using? She's away from the rest of the flock now. Will this kill her?

VetRx is useless against respiratory diseases. You could possibly be dealing with Infectious Coryza, Mycoplasma Gallisepticum (MG,) or Infectious Bronchitis (IB.) Here's a link explaining each of these diseases with treatments etc...However, if in fact it's a respiratory disease, I recommend you cull the sick bird.http://edis.ifas.ufl.edu/ps044

I just bought this for my little girl Nori. She has been dealing with this dang cough/sneeze for a couple weeks now. I started with Metronidazole and that didn't help, then I tried Doxycycline and that didn't work either. So I went out and bought this today. I explained her symptoms to the girl at Tractor supply (sneezing/coughing but no watery eyes or discharge) and she said a lot of people have had great success with this. I didn't realize it was made with essential oils, I have been looking into using these for all natural remedies and I really hope it works. She was not a fan of having it dripped into her nose and was coughing a lot but so would i , I rubbed it all over her as well as her friend who is with her. It has been very quiet the past couple minutes, just had to go make sure she was still alive haha! I will let you know if it works, seeing as other medicines have not. I am also going to use it in a nebulizer so she can breathe it in without choking on it Just have to get it from my dad. Here's to hoping!

Edit: I do realize she may have a respiratory fungal infection, but I don't have money to order and ship oxine right now so I am trying this first. She does not show she is in much distress so I am not super worried. Just want this dang cough to go away before the show next month! And it is not contagious, because her friend is not doing it and they have been together the whole time.

Please keep me posted on Nori. I'll be interested to know how long her recovery takes. Hope continues to do better, but is still not 100%. However, she is no longer wheezing like she was, nor is there anything wrong with her eyes now. She is also eating and drinking normally, but still seems tired. I have been observing the flock closely and no one else seems to have this. I am wondering if she really had/has a cold if none of the other chickens are sick. She's three months old and still too young to lay, but could this be related to getting ready to lay? I have no idea whether I should put her back with the flock or not since she is doing so much better. If anyone else has had anything similar like this, could you let me know? I would take her to the vet, but it doesn't seem to make sense to do so since she's on the mend. Also, the nearest chicken vet is an arm and leg.